Heretofore, semiconductor devices with an Al/SiO2 multilayer interconnect structure, which uses Al, Al alloy or the like as an interconnect material, and uses an SiO2 film as an interlayer dielectric, have been mainly manufactured. In recent years, in order to reduce the interconnect delay caused by the miniaturization of semiconductor devices, semiconductor devices with a Cu/low-k multilayer interconnect structure, which uses Cu with low resistance as an interconnect material and a low-k film (a low dielectric constant film) with low interconnect capacitance as an interlayer dielectric, are being manufactured in large quantities.
Cu/low-k multilayer interconnect structures are produced by a process called damascene. In this process, an interconnect structure is obtained by forming trenches or holes (via holes) in an interlayer dielectric substrate, and then filling the trenches or holes with an interconnect material such as Cu.
In a process called dual damascene, trenches for an interconnect and via holes are formed continuously in an interlayer dielectric substrate made of a low-k film or the like, and then filled with an interconnect material such as Cu. A dual damascene structure can be formed by a via-first process, wherein via holes are formed prior to trenches for an interconnect; or conversely, by a trench-first process, wherein trenches for an interconnect are formed prior to via holes; or by other processes such as a middle-first process or a dual hard mask process.
In, for example, processes such as the via-first process via holes are formed in an interlayer dielectric substrate by dry etching, and then filled with a filling material and planarized. Lithography is subsequently performed to form trenches, and dry etching follows. Subsequently, ashing or a like process is performed to remove unwanted substances such as resist or filling material from the substrate having trenches and via holes.
Even after this process, however, unwanted substances (hereinafter referred to as “residues after a dry process”) that cannot be completely removed remain on the substrate.
Moreover, dry processes using plasma, such as dry etching and ashing, cause damage to Cu used as the interconnect material and the low-k film as the interlayer dielectric. Further, when the substrate is exposed to air while being transferred from one process to another, a Cu oxide film is formed on the surface of the Cu metal interconnect.
In a damascene structure, when trenches and via holes are filled with TaN as a barrier metal and metals such as Cu as an interconnect material, the presence of residues or Cu oxide film after a dry process leads to defective semiconductor devices. For this reason, these residues are typically removed using a polymer-removing solution. Because the damaged low-k film is structurally more fragile than the original, it is easily etched by a chemical solution or the like, and undergoes changes in pattern dimensions. Thus, during removal of these residues, it is necessary to prevent the corrosion of Cu caused by the chemical solution, and inhibit etching of the low-k film.
When commercially available known polymer-removing solutions or etchants are used to remove the residues and Cu oxide films after a dry process, problems with workability arise. For example, the residues can be removed using hydrochloric acid or fluoric acid diluted with water, but a large number of dissociated H+ tend to cause Cu corrosion. Moreover, if the interlayer dielectric film (especially when it is a porous low-k interlayer dielectric film) has been damaged by dry etching, the surface condition of the interlayer dielectric may be degraded by etching, or the substrate cannot be processed to the dimensions as designed.
Further, dry processes are becoming more diverse due to the miniaturization of device structures, different types of low-k films, and the like. For example, in addition to known dry processes such as dry etching using a resist mask and ashing using oxygen plasma, dry processes such as dry etching using a hard mask and ashing using He/H2 plasma are now being used. Along with such changes, there is a desire for the residues and Cu oxide films after a dry process to be selectively removed without damaging Cu or low-k films.
Low-k films, however, are often damaged by a dry process; and, when cleaned with a polymer-removing solution, they are thus easily etched and undergo changes in pattern dimensions. Further, apparatuses for cleaning semiconductor devices are changing from batch-type apparatuses to single-wafer-type apparatuses. Accordingly, with a method that uses a known removing solution, it is difficult to completely remove, in a short period of time, the residues after a dry process, which strongly adhere to the Cu/low-k structure. Although the Cu bulk is not corroded by cleaning, a close examination thereof often reveals the presence of cracking and roughness along the grain boundaries of the Cu surface. It is very likely that the device performance is adversely affected by the minor cracking and roughness of the Cu surface. Further, the growth of Cu oxide films caused by exposure of processed wafers to air after the cleaning process may also cause device defects.
When Cu/low-k multilayer interconnect structures are formed using known chemical solutions such as hydrochloric acid and fluoric acid, it is difficult to inhibit Cu corrosion and etching of low-k films, and to selectively remove the Cu oxide films and residues after a dry process.
Polymer-removing solutions intended for Cu/low-k multilayer interconnect structures have recently been developed (for example, Patent Literatures 1 to 4). With these polymer-removing solutions, however, it is difficult to inhibit Cu corrosion and completely remove the residues after a dry process in a short period of time without damaging the low-k film. Further, it poses a greater challenge to inhibit cracking and roughness of the Cu surface.
In view of the above-described current situation, the inventors of the present invention proposed a chemical solution capable of inhibiting cracking and roughness of the Cu surface without damaging Cu and low-k films, and that is also capable of removing the residues after a dry process in a short period of time (Patent Literatures 5 and 6).
Today, however, there is a demand for a polymer-removing solution for higher quality Cu/low-k multilayer interconnect structures. Specifically, it is necessary to prevent Cu corrosion and minimize cracking and roughness of the Cu surface while causing little damage to newly introduced porous low-k films. In order to prevent further roughness of the Cu surface, it is imperative to leave, rather than remove, a Cu thin film layer, which is formed on the Cu surface as a result of damage during a dry process after residues are removed by the chemical solution. Additionally, methods for leaving this thin film as a protection film until the next process are spreading. Leaving the thin film is considered to be useful for improving the yield. There is a demand for a polymer-removing solution that satisfies the above-described requirements and that can completely remove residues after a dry process in a short period of time.